The present invention relates to integrated circuit packages, and more particularly to an integrated circuit package having beam leads approaching die bonding pads from more than one direction.
Semiconductor chips or wafers are used in applications including integrated circuits (ICs) or flash memory, which may be used in portable electronic devices. It is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area to minimize the size, weight, and energy consumption of devices using the semiconductor chips. ICs, whether individual active devices, individual passive devices, multiple active devices within a single chip, or multiple active and passive devices within a single chip, require suitable input/output (I/O) connections between themselves and other circuit elements or structures. These semiconductor devices are typically small and fragile and commonly carried on substrates or carrier members for support. These devices are also frequently encapsulated to protect the device from unfavorable environments, such as dust, mechanical or electrical loads, and moisture.
As the density of semiconductor chip integrated circuits increases, the density of I/O terminals, such as contacts and leads must also increase through, for example, smaller contacts and leads and/or different I/O configurations. Chip-scale packages (CSPs) offer one advantageously compact geometry, requiring a package having dimensions no more than 1.2 times the dimensions of die 10. CSPs find particular applicability in portable devices such as pagers, camcorders, cell phones, cameras, personal information managers, laptop computers, and global positioning devices, where size and weight are important considerations. Of these chip-scale packages, one increasingly important high density I/O configuration is a micro-ball grid array (xcexcBGA) package. FIGS. 1 and 2 illustrate a chip-scale xcexcBGA package.
FIG. 1 shows a cross-section of the xcexcBGA package including a die 10, an elastomer or epoxy-based thermoset adhesive 20 applied to a lower surface of die 10, and a tape or sheetlike interposer 30, such as an insulating organic film of polyimide. The tape 30 has an adhesive 25 formed on one side and also has metal traces or wirings 40 formed thereon or embedded therein. The metal traces 40 are made, for example, by forming a thin metallic film on the tape 30 such as by evaporation or deposition and wet-etching the metallic film. At one end, each of the metal traces 40 is attached to a respective die bonding pad 60. The traces 40 are routed across tape 30, as shown in FIG. 2, to terminate in a conductive land 45. The lands 45 collectively form a matrix pattern and vias or holes 50 are formed in the tape 30 to overlie these lands 45. As shown in FIG. 1, conductive balls 65 such as solder balls are formed in vias 50 to contact lands 45 and permit electrical connection of the I/O terminals or bonding pads 60 of the die 10 to corresponding bonding pads disposed on the surface of a printed circuit board (PCB) or other substrate. The pitch, a distance from a center line of one ball to a center line of an adjacent ball, is designated by P. An encapsulant 80, such as an epoxy thermoset, is provided to protect the electrical connections from damage caused by unfavorable environments, such as described above.
As shown in FIG. 2, tape windows 70 are selectively formed at either end of die 10 in areas corresponding to the die I/O bonding pads 60. Subsequent to connection of tape 30 to die 10, traces 40 are connected to bonding pads 60. One approach to connecting trace 40 and bonding pad 60 is xe2x80x9cwire bondingxe2x80x9d, wherein a separate wire is used to connect a bonding pad provided at an end portion of trace 40 to bonding pad 60. The separate wire is bonded to each of the bonding pads by bonding means including ultrasonic bonding, thermal bonding, and compression bonding. Another approach to connection of traces 40 and bonding pads 60 which is better suited for the particular design constraints of xcexcBGA and limitations of conventional manufacturing equipment, is a xe2x80x9cbeam leadxe2x80x9d connection illustrated by FIGS. 1 and 2. The beam lead connection is achieved by forming a portion 55 of each trace 40 to project into tape window 50 and overlie a position to be occupied by a bonding pad 60. When a die 10 is disposed in a die receiving area 15 of tape 30, the bonding pads 60 are exposed within the tape window 50 and are displaced (e.g., vertically) from a projecting portion 55 of a corresponding trace 40. The projecting portion 55 is mechanically deformed (e.g., vertically) to contact a bonding pad 60, where it is bonded to the bonding pad 60 by conventional bonding techniques and tools, such as an ultrasonic wedge bonder, to form a beam lead connection.
FIG. 3 illustrates a non-linear distribution of die bonding pads 60 wherein two groupings of bonding pads are disposed substantially perpendicular to one another. As with the previous example, a portion 55 of each trace 40 projects into tape window 50 to overlie a bonding pad 60. Portions 55 span a width of the tape window 50 or project into the tape window from the side and terminate in a tie bar or beam lead support 75. The tie bar 75 is typically a ganged support common to a plurality of beam leads. To form an electrical connection between the portion 55, or beam lead, to the die 10 bonding pad 60, the portion 55 is mechanically deformed to contact a respective bonding pad 60. This deformation and bonding may be achieved by conventional bonding techniques and tools, such as an ultrasonic wedge bonder, thermode, or thermosonic bonder to form the beam lead connection. Portions 55 may have a notch adjacent tie bar 75 to facilitate separation of the beam lead 55 from the tie bar 75 during formation of the electrical contact.
However, despite its advantages, xcexcBGA packaging is not as robust as conventional packaging and die evolution to increasingly smaller die sizes, particularly to CSPs, imposes additional constraints on design, manufacture and reliability of the die packaging. One important parameter is the bending profile of the beam lead, the exposed portion of the trace 40 extending into the tape window 70 to contact the die 10 bonding pad 60. If the bending profile, such as the radius of curvature of the points of beam inflection, is too severe hairline cracks may develop and lead to device failure. Conventionally, to ensure that the beam lead bending profile is maintained, a predetermined tape window 70 size or width is kept constant and a predetermined beam length is maintained.
Dies may be designed with a non-linear distribution of bonding pads. For example, bonding pads 60 may be distributed around a comer of the die 10, as shown in FIG. 3. In such a case, beam leads 55 may be required to approach the die bonding pads from more than one direction. Conventionally, a tie bar or beam lead support 75 is formed to support and maintain the beam lead protruding portions 55 above a corresponding bonding pad 60 until they are separated from the tie bar during the bonding operation. However, xcexcBGA design rules require both a minimum space S between pads on adjacent sides of about 0.2 mm and require a minimum beam lead length L of about 0.9 mm, although the actual requirement may vary. These requirements, combined with the conventional reliance on a tie bar or beam lead support to preserve alignment of the beam leads during packaging and the requisite tolerances necessary to ensure that the beam lead support will not inadvertently short circuit a beam lead adjacent and parallel thereto, sacrifice valuable die and packaging space.
Accordingly, a need exists in the art for an improved ball grid array package that avoids a potential for short circuit due to beam lead support placement and provides additional flexibility in bonding pad and beam lead placement.
This and other needs are met by the invention which provides, in one aspect, a tape automated bonding (TAB) tape including an insulating tape having a die receiving section and a conductive wiring pattern forming a plurality of traces including a land at one end and a beam lead at another end. A tape window is formed in a portion of the tape die receiving section. At least one trace beam lead extends over the tape window from a first direction and is connected to a tie bar adjacent an opposing side of the tape window and at least one trace beam lead extends over the tape window from a second direction different than the first direction and is cantilevered over the tape window.
Another aspect of the invention is a method for manufacturing a semiconductor package. This method includes providing an insulating tape including a die receiving section for a predetermined die and forming a conductive wiring pattern on or in the insulating tape, including a plurality of traces comprising a land at one end and a beam lead at another end. A tape window is formed in a portion of the die receiving section corresponding to a location of a plurality of die bonding pads of the predetermined die. At least one trace beam lead is formed to extend over the tape window from a first direction and connect to a tie bar adjacent an opposing side of the tape window and at least one trace beam lead is formed cantilevered over the tape window from a second direction different than the first direction.
Included within the above aspect of the invention are additional steps of providing the predetermined die bearing a plurality of bonding pads, placing the predetermined die and the insulating tape adjacent one another to juxtapose the tape widow and the bonding pads and align the bonding pads to corresponding beam leads. A portion of the trace beam lead formed to extend over the tape window from a first direction in displaced in a direction of a corresponding bonding pad to separate the trace beam lead from the tie bar and abut said portion against the bonding pad, where they are electrically connected and a cantilevered portion of the trace beam lead cantilevered over the tape window from a second direction is displaced in a direction of a corresponding bonding pad to abut said portion against the bonding pad, where they are electrically connected.